Stellar density and bar strength should affect the temperatures of the
cool (T ~ 20-30 K) dust component in the inner regions of galaxies,
which implies that the ratio of temperatures in the circumnuclear
regions to the disk should depend on Hubble type. We investigate the
differences between cool dust temperatures in the central 3 kpc and disk
of 13 nearby galaxies by fitting models to measurements between 70 and
500 μm. We attempt to quantify temperature trends in nearby disk
galaxies, with archival data from Spitzer/MIPS and new observations with
Herschel/SPIRE, which were acquired during the first phases of the
Herschel observations for the KINGFISH (Key Insights on Nearby Galaxies:
a Far-Infrared Survey with Herschel) sample. We fit single-temperature
modified blackbodies to far-infrared and submillimeter measurements of
the central and disk regions of galaxies to determine the temperature of
the component(s) emitting at those wavelengths. We present the ratio of
central-region-to-disk-temperatures of the cool dust component of 13
nearby galaxies as a function of morphological type. We find a
significant temperature gradient in the cool dust component in all
galaxies, with a mean center-to-disk temperature ratio of 1.15 ±
0.03. The cool dust temperatures in the central ~3 kpc of nearby
galaxies are 23 (±3)% hotter for morphological types earlier than
Sc, and only 9 (±3)% hotter for later types. The temperature
ratio is also correlated with bar strength, with only strongly barred
galaxies having a ratio over 1.2. The strong radiation field in the high
stellar density of a galactic bulge tends to heat the cool dust
component to higher temperatures, at least in early-type spirals with
relatively large bulges, especially when paired with a strong bar.
Herschel is an ESA space observatory with science instruments provided
by the European-led Principal Investigator consortia and with important
participation from NASA.